Introduction
The International Date Line and the Halachic Date Line, known as Kav Hataarich,
are similar in nature, yet they might be in different places on the map.This article will go into the location of the Halachic Date Line and the
difference between it and the International Date Line, and some Halachot that
apply to one who crosses the Halachic Date Line.For a full Halachic discussion of this issue see the twenty second volume
of the Encyclopeida Talmudit.

International
Date Line
The International Date Line is an imaginary Line on the 180th
meridian in the Pacific Ocean that goes through the Bering Strait (between
Alaska and Russia), which is half way around the world from Greenwich, England.It is basically a straight Line; however, there are some zigzags.These zigzags are necessary because otherwise one country would be
observing two Dates at the same time.In
order to prevent this, the International Date Line curves around these countries
and only goes through the Pacific Ocean [1] (See Fig.1).Its purpose is to be a separation between two consecutive calendar days,
the old day and the new day.So if
one were to go west of the International Date Line, he would be in the new day.However, if he were to go east of it he would be in the old
day.The old day stretches from the
International Date Line eastward until it reaches the spot where midnight begins
(See Fig.2).The International Date
Line, which is “attached” to the Earth, moves towards midnight as the Earth
turns.Once the International Date
Line reaches midnight, in effect for that moment the entire world is under one
day.However, once the
International Date Line passes through midnight, the new day begins to spread
between midnight and the International Date Line, and the old day gets smaller
as the process is being repeated [2].This
is the separation that is accepted in the secular world, but not necessarily in
the Halachic World.

Location of the
Halachic Date Line
The Halachic Date Line is possibly different than the International Date Line.The reason for this, is that the current International Date Line was
rather arbitrarily drawn in 1921 by the British Admiralty [1], while certain
Gedolim such as the Baal Hamaor who lived in the 12th century refer
to the Halachic Date Line.So, on
the topic as to the location of the Kav Hataarich there is much debate amongst
twentieth century Poskim, including the Chazon Ish, Rav Yechiel Michel
Tukatzinsky, Rav Isser Zalman Meltzer, Rav Yonassan Shteif, the Sefer Haibur,
Rav Dovid Shapiro, and Rav Yonah Merzbach [3].

The earliest authority to address this issue
is the Baal Hamaor.He brings up
the topic based on a Gemara (Rosh Hashanah 20b) regarding the topic of Kiddush
Hachodesh, the sanctification of the new month.The Baal Hamaor explains that Bait Din has until noon on the day that
they see the molad, new moon, to declare Rosh Chodesh on that same day.However, if it is after noon, then Rosh Chodesh is on the next day.This explanation would only make sense if the Halachic Date Line was at
the Kitze Hamizrach which is 90° east of Jerusalem.This is so because the reason why the Baal Hamaor said noon is because
that is the last time in Israel that somewhere else in the world that the day is
just starting.In order for Rosh
Chodesh to be on that day, it must be possible for Rosh Chodesh to last 24 hours
somewhere in the world.Since noon
is 18 hours into the day (starting from sunset on the night before), the place
where the day is just starting is 18 hours to the west of Israel which is 270°
west of Israel because every time zone is made up of 15°.So, the place where the new
day starts, or the Halachic Date Line, must be six hours to the east of
Jerusalem which is also 90° east of Jerusalem.This Line is on the 125E meridian [4].

The modern question, as to the location of
the Halachic Date Line, was presented to the Chazon Ish in a letter sent to him
in Israel in 1941 by students of Mir and Chachmei Lublin that fled from Europe
to Japan.The students knew that
according to the Baal Hamaor the Halachic Date Line is on the 125E meridian and
Japan is on the 140E meridian.So,
they knew that they must have crossed the Date Line, meaning that they went back
one day.For example, if they
crossed on Sunday then it is now Shabbat in Japan according to Halacha, even
though the local population considers the day as Sunday (since it was west of
the secular DateLine).The
students’ question was regarding Yom Kippur in 1941 which fell out on a
Wednesday.If they had indeed
crossed the Halachic Date Line, then perhaps they should observe Yom Kippur on
the Japanese Thursday which is the Halachic Wednesday. The Chazon Ish responded
to the students of the Mir Yeshiva including Rav Yechezkel Levenstein, Rav Chaim
Shmulevitz, and Rabbi Alex Weisfogel that they had crossed the Halachic Date
Line.According to the Chazon Ish,
the principle of the Baal Hamaor is correct; the Halachic Date Line is at the
Kitze Hamizrach, but it can not cut through land because then one person will be
observing one day while his neighbor is observing another day.So, he says that the Halachic Date Line is at the end of the continent on
the border between the coast and the Pacific Ocean so that it does not cut
through any land (See Fig.3) [3].Thus,
all of Australia is considered to lie west of the Halachic DateLine even though
much of Australia lies east of the Halachic DateLine.

Based
on the same question raised by the students of the Mir Yeshiva and Yeshivat
Chachmei Lublin, Rav Yechiel Michel Tukatzinsky, who was the leading
calendar expert in Israel at the time, answered that the students of the
Yeshivat Chachmei Lublin should fast on the Japanese Wednesday because they did
not cross the Halachic Date Line.Rav
Tukatzinsky rules that the Halachic Date Line is based on Jerusalem being the
center of the world and it is the starting point where east and west is referred
to.So, the spot on the Earth where
the day Halachically starts is half away around the world, 12 hours or 180°
east of Jerusalem.This is the Halachic Date Line which is at the 144.8W
meridian (See Fig.3).This is the
most widely accepted opinion as to the location of the Halachic Date Line, but
according to him, half of Alaska is west of the Date Line.So, by using the Chazon Ish’s principle of stretching the Line on to
the border, all of Alaska is east of the Halachic Date Line [3].In addition, Hawaii lies west of the Halachic Date Line according to this
opinion, even though it is west of the secular Date Line.

Rav Isser Zalman Meltzer and Rav Zvi Pesach
Frank (Teshuvot Har Zvi 1:138) claim that there is no such thing as a
Halachic Date Line.Instead, a
person just follows the day that the country that he is in is observing.For example, if in Japan it’s Wednesday, then the person
views the day as the halachic Wednesday [3].So, they would answer the students that they should observe Yom Kippur on
the Japanese Wednesday.Also, since
the world adopted the International Date Line as the point where the day begins,
in essence they would say that this too is the Halachic Date Line.Rav Yonatan Shteif would also probably agree based on the fact that he
says that the Halachic Date Line is based on the day that the country
traditionally observes [3].

The Sefer Haibur says that the center of the
world is 24° east of Jerusalem.So
using the principle of the Baal Hamaor, that the new day starts six hours east
of the starting point, the Halachic Date Line is 114° east of Jerusalem, which
is on the 149E meridian (See Fig.3) [3].

Rav David Shapiro believes that the Halachic
Date Line is very close to the International Date Line.There is a Midrash that says that the sun first appeared in Jerusalem in
the beginning of the fourth hour.So,
the sun first appeared in the world three hours or 45° east of Jerusalem.However, the day starts at sunset, which is another six hours or 90°
east.In total, sunset, or the
beginning of the first day, took place nine hours or 135° east of Jerusalem.However, most poskim hold that a day halachicly begins at nightfall,
tzeit hakochavim, which is approximately 8° east of sunset.In total, the spot where day began on the first day is 143° east of
Jerusalem, which is on the 178E meridian.This
is within two degrees of the International Date Line, which is on the 180th
meridian.So basically according to
Rav David Shapiro, the Halachic Date Line is the International Date Line [3].

According to Rav Yonah Merzbach and Rav
Binyamin Rabinowitz- Tevmim, the Halachic Date Line is at the easternmost point
of Asia, which is the tip of Siberia and the Bering Strait.This Line is on the 170W meridian, which is ten degrees east of the
International Date Line (See Fig.3) [3].

Although there are many opinions as to the
location of the Halachic Date Line, most Poskim consider three possibilities
when applying halachic decisions.Either
the Chazon Ish, which is the Baal Hamaor but the extension to the coast is
added, Rav Tukatzinsky, and Rav Isser Zalman Meltzer.

HalachotThere are various areas of Halacha emerge from the Halachic Date Line
issue.There are many mitzvot that
are related to time and day that are effected by someone who crosses the
Halachic Date Line.Three of the
most common ones are Tefila, Sefirat Haomer, and Tefilin.However, in order to discuss these topics, one specific
Halachic Date Line must be used.Even
though there are various opinions as to the location of the Halachic Date Line,
Rav Tukatzinsky’s is the most widely accepted one.So, that is the one that will be taken into consideration when discussing
the crossing of the Halachic Date Line.However, each one of these mitzvot can be discussed for each
opinion.

Tefila
Because Tefila or prayer occurs at least three times every day, it is one of the
most frequently brought up questions when dealing with Date Lines.There are two related questions that are based on the direction in which
the Date Line was crossed.First of
all, a person traveling from east to west would be going into a new day.For example, if he left Los Angeles on Sunday at 6:00 AM, when he gets to
Tokyo it will be 11:00 AM on Monday because of the 17 hour time difference and
the 12 hour flight [5].So, if he
davened Shacharit on Sunday in Los Angeles, must he daven Shacharit on Monday in
Tokyo even though he has not experienced a new sunrise?Another question that arises is from a similar scenario.A person traveling from west to east would be going back one day, and
might experience sunrise as after he crosses the Date Line.For example, if a person leaves Tokyo at 3:00 PM on Monday he will get to
Los Angeles at 7:00 AM on Monday morning because of the 17 hour time difference
and the nine hour flight [5].So,
during his flight he experienced sunrise on Monday morning for a second time,
yet he already davened Shacharit on Monday morning.Must he daven Shacharit again? [3]

Regarding the first case Rav Betzalel Stern
in his sefer, Teshuvot Betzel Hachochma, explains that one’s obligation
to daven is based on their personal day.In
other words, every time a person experiences sunrise they are obligated to daven
Shacharit, and every time they experience sunset they are obligated to daven
Ma’ariv.In this case, since he
did not experience a new sunrise, he does not have to daven Shacharit a second
time.A second opinion is given by
Rav Yechezkel Roth in sefer, Teshuvot Emek Hateshuva, who says that
one’s obligation to daven Shacharit is only once a day, and once it has been
fulfilled the next obligation only comes the next day.For example, the obligation to eat Matzo on Pesachis only once a
year, and once it has been completed the next obligation only comes the next
year.So, in this case even though
he did not experience sunrise, his obligation to daven Shacharit on Monday was
not fulfilled, and he must daven Shacharit again [3].

On the other hand, regarding the second case
Rav Stern says that since he did experience sunrise he must daven Shacharit
again in order to fulfill his obligation.However,
Rav Roth says that since it is still the same day of the week (Monday), even
though he experiences two sunrises, he does not have to daven Shacharit again
[3].For practical Halacha, anytime
one experiences a sunset and then a sunrise must daven Shacharit after sunrise.However, if one does not experience a sunrise then he should just recite
the Shir Shel Yom for the day that he flies into [6].

Sefirat
HaomerThere is a mitzva in the Torah to count 49 days at night with a bracha,
beginning with the second night of Pesach.If one forgets to count at night, he may count in the morning
without a bracha and then can continue to count from that night on with a
bracha.However, the Shulchan Aruch
rules that if one goes an entire day and night without counting, he can no
longer count with a bracha.So, if
one were to cross the Date Line from east to west, he will be going into a new
day and one day is lost.For
example, a person who leaves New York on Sunday night and counts for Monday on
Sunday night (as is the Halacha), and then will reach Tokyo on Tuesday morning
(as there is a 14 hour time difference and it is a 18 hour flight), should count
for Tuesday on Tuesday morning when he crosses the Date Line without a bracha,
and then continues to count that night with a bracha.However, if one crosses the Date Line from west to east, the
day repeats itself.For example,
one who leaves Tokyo on Monday afternoon will get to Los Angeles on Monday
morning.Since he counted on Sunday
night for Monday in Tokyo, when he gets to Los Angeles he should count for
Monday without a bracha and then continues counting on Monday night with a
bracha [3].

TefilinThere is a mitzva in the Torah to wear Tefilin, and they are worn every
day.However, questions arise when
one crosses the Date Line and is not sure whether or not he should put on
Tefilin again.In order to answer
the question there are two ways to look at the mitzva of Tefilin.If it is a daily mitzva that is only done once a day, then it is subject
to the disagreement between Rav Stern and Rav Roth regarding tefila.Tefilin is simply substituted for tefila, and the Halacha would be that
any time sunrise is seen Tefilin are worn.Regarding a bracha, a bracha is said every time Tefilin are put on
because they can be worn many times during the day.So, one who is crossing the Date Line from east to west, from
Los Angeles to Tokyo, should put on Tefilin when he crosses the Date Line of it
is light outside.The reason for
this is because if there is doubt as to whether or not one should put on Tefilin,
it is okay to put them on because they can be worn many time during the day.If one is crossing the Date Line from west to east, from Tokyo to Los
Angeles, he should only put on Tefilin, if he experiences sunrise because
other wise he already put them on once after a sunrise, i.e. before he left
Tokyo [3].

ConclusionThe International Date Line and the Halachic Date Line might be in two
different places, but they both serve a similar purpose.They both separate between two different days.In the world of Halacha it is very important to know where the Halachic
Date Line is because so many mitzvot are attached and dependent on time.Tefila, Sefiras Haomer, and Tefilin are just three of the most common
ones that are part of a long list.One
should consult with his Rav should he need to travel to any part of the world
that is subject to this dispute.